1. Field of the Invention
The present invention relates to an abnormality determining apparatus for determining the presence of an abnormality in a detection subject on the basis of stored information stored in information storage means, and a result obtained by information obtaining means for obtaining information about an object, and also to an abnormality determining method and an image forming apparatus.
2. Description of the Background Art
In an image forming apparatus such as a copier, facsimile device, or printer, maintenance is required to replace consumables (toner, for example) and components (a photosensitive body, for example), repair faults, and so on. When a fault occurs, all or a part of the functions of the device must be halted from the occurrence of the fault to the completion of repairs, causing a great time loss for the user. It is therefore desirable to predict the occurrence of a fault in the image forming apparatus, the end of the life of a component, and so on in order to provide the user with a maintenance preparation period, thereby reducing the amount of downtime. Examples of an image forming apparatus which is capable of making such predictions include the device disclosed in Japanese Unexamined Patent Application Publication H5-281809 (Prior Art 1), for example.
In the image forming apparatus disclosed in this Prior Art 1, driving load information regarding a driving source is detected, and early detection of an abnormality in the driving system is performed by comparing the detection result with a standard value. According to this constitution, by detecting an abnormality in the driving system before a fault occurs, a user can be provided with a preparation period to prepare for maintenance to the driving system.
A Mahalanobis Taguchi System, described in the Japanese Standards Association publication “Technical Developments in the MT System” by Genichi TAGUCHI (Prior Art 2), is known as a method of measuring the degree of normality in the state of an object. This MTS method measures the degree of normality in the state of an object in the following manner. First, a plurality of combined normal values relating to a group of information comprising a plurality of types of information indicating the state of a detection subject is obtained, and a normal group data set is constructed therefrom. To take a medical examination as an example, first combined normal values comprising the gender, various blood test results, height, weight, and so on of a healthy person are obtained in advance from a plurality of healthy people, and a normal group data set is constructed therefrom. Next, a multidimensional space is constructed on the basis of the normal group data set. The Mahalanobis distance, which indicates the position of the grouped information obtained from the detection subject in this multidimensional space, is then determined, and an evaluation is performed to determine the degree of similarity between the grouped information for the detection subject and the normal group data set. According to this MTS method, the degree of normality of the detection subject can be determined comprehensively on the basis of the correlation among the various information.
The image forming apparatus disclosed in the aforementioned Prior Art 1 detects in particular driving system abnormalities caused by an excessive load being placed on the driving source. Abnormalities in the driving system may have numerous other causes. Any abnormality can be detected by monitoring the presence of its cause. However, if the presence of the cause of each abnormality is monitored and detected individually, the control required for this monitoring becomes extremely complicated, and as the number of types of abnormality to be detected increases, the control becomes ever more complicated.
Hence the present inventors are currently developing a novel image forming apparatus which is used to determine an abnormality by determining the Mahalanobis distance according to the aforementioned MTS method, on the basis of a normal group data set stored in information storage means and the results obtained by sensors and the like of a plurality of types of information. According to this image forming apparatus, the degree of normality is evaluated on the basis of a Mahalanobis distance determined from a plurality of types of information relating to various abnormalities, rather than detecting a plurality of abnormalities individually according to the presence of their respective causes, and hence the occurrence of these abnormalities can be detected comprehensively. In so doing, the complicated control required to detect a plurality of abnormalities individually according to the presence of their respective causes can be avoided.
However, since this image forming apparatus detects the occurrence of various abnormalities comprehensively by perceiving the degree to which the apparatus has deviated from a normal state, it is difficult to specify the type of the abnormality. As a result, the maintenance response following the detection of the abnormality becomes complicated.
Further, a remote fault diagnosing system is installed in the image forming apparatus disclosed in the aforementioned Prior Art 1. In this remote fault diagnosing system, basic diagnosis data transmitted from a plurality of image forming apparatuses serving as diagnosis subjects are received in a central diagnosing apparatus, and various abnormalities in the individual image forming apparatuses are diagnosed on the basis of these basic data. These various abnormalities include a paper feeding abnormality, an image quality abnormality, and so on. By diagnosing the various abnormalities respectively, a fault in the paper feeding system or image forming system caused by the progression of the diagnosed abnormality can be predicted before its occurrence. Moreover, when diagnosing the various abnormalities, the remote fault diagnosing system takes into account the proficiency of the user of the image forming apparatus and the degree of perception of the fault. This is due to the following reason.
For example, a user who is highly conversant with the image forming apparatus may be able to repair a fault in the image forming apparatus that a general user could not repair. In such a case, the user would not contact a repair service organization to request repairs. If a serviceperson is dispatched nevertheless due to the prediction of the occurrence of the fault, the resulting wasted labor would lead to an increase in service costs. Moreover, depending on the type of fault, each user has a widely differing perception thereof. For example, one user may suspect a fault in the paper feeding system even when a paper jam occurs rarely, whereas another user may not suspect a fault in the paper feeding system even when paper jams occur comparatively frequently. In the case of the latter user, repair requests are rarely made, even if a serviceperson is dispatched at the stage when the abnormality in the paper feeding system has barely begun to occur. This manner of dispatch also leads to an increase in service costs. Hence by taking into account the proficiency and degree of fault perception of the user, abnormality diagnosis which is suited to each individual user is performed, leading to a reduction in service costs. Note that as a result of dedicated research, the present inventors have discovered that, from among various abnormalities, the degree of perception of each user varies particularly widely in regard to an abnormality in the image quality.
This remote fault diagnosing system diagnoses each of a plurality of abnormalities occurring in the diagnosis subject image forming apparatus individually. Hence as the number of types of abnormality to be diagnosed increases, the calculation amount required for the diagnosis increases, making control more complicated. Moreover, providing the user with a preparation period required to prepare for maintenance in order to reduce downtime is desirable not only in an image forming apparatus, but in various other apparatuses such as manufacturing devices and electric appliances.
Hence the present inventors are currently developing a novel abnormality determining apparatus in which various abnormalities in a detection subject such as an image forming apparatus are determined comprehensively as a single general abnormality, rather than individually. The presence of the general abnormality is determined on the basis of the aforementioned Mahalanobis distance, for example. According to the abnormality determining apparatus constituted in this manner, when at least one of the various abnormalities occurs, the general abnormality is determined comprehensively as “abnormality present”, and thus increasingly complicated control due to an increase in the number of types of abnormality in the determination subject can be suppressed.
However, when the general abnormality is determined as “present” using a method of perceiving the degree of deviation from a normal state, as with the Mahalanobis distance, rather than perceiving the presence of individual abnormalities, it is difficult to specify the type of abnormality that has occurred from among all of the abnormalities that may be incorporated into the general abnormality. As a result, the maintenance response following a determination of “general abnormality present” becomes complicated.
Furthermore, the abnormality determining apparatus is unable to determine various abnormalities in consideration of the user's proficiency and degree of fault perception. As a result, even when an attempt is made to specify the type of the abnormality that has occurred, the abnormality determination precision is not always suited to the user, and depending on the user, abnormalities may be detected unnecessarily, the detection timing may be too late, and so on.
In an image forming apparatus disclosed in Japanese Unexamined Patent Application Publication H05-100517 (Prior Art 3), the life of a photosensitive body is predicted by monitoring the potential state of the photosensitive body. More specifically, forecasts are made regarding faults in and the lifetime of limited locations within the system that monitors this information. This is an important process in itself, but with this method, although it is possible to determine abnormalities in the monitored locations, it is not possible to predict device problems having multiple causes. Particularly in this case of an electrophotographic image forming apparatus, balance is maintained over the entire apparatus by means of control in which process parameters are moved as a whole through process control, and hence it is impossible to determine abnormalities simply by monitoring a single piece of information.
Further, in an image forming apparatus disclosed in Japanese Unexamined Patent Application Publication H08-137344 (Prior Art 4), the state of the image forming apparatus is determined by detecting a check pattern on a photosensitive body to determine whether or not the image thereof is normal. With this method, abnormalities on the upstream side of the image forming operation, including the photosensitive body, can be determined in composite, but abnormalities on the downstream side cannot be determined at all.
Meanwhile, it is also possible to obtain a plurality of types of information expressing the state of an image forming apparatus, calculate a single index value from the plurality of types of information, and determine a change of state in the image forming apparatus on the basis of temporal variation data of the index value. With this method, if information is obtained in advance for each location of the apparatus as the plurality of types of information, the overall operational state of the apparatus can be monitored at all times. Further, when the plurality of types of information varies as a whole, the apparatus can be determined as normal if the information varies as a whole while maintaining a normal balance, and determined as abnormal if not. The important point of this state determining method is that “a calculation parameter for calculating an index value is determined using only a plurality of types of data gathered when the image forming apparatus is in a normal state”. The calculation parameter is a reference expressing a normal state, whereas the index value, which is calculated after the calculation parameter is fixed using temporal momentary data (or the average data of a fixed time period), has a characteristic whereby it becomes larger as the image forming apparatus moves further from a normal state. Thus the location of the image forming apparatus which is moving toward an abnormality can be determined.
A problem which arises at this time is “when should the calculation parameter be fixed?”. In such a determination, it is presumed that a normal data set obtained in a factory environment prior to shipping, for example, would be insufficient. This is because an actual usage environment on the market is considered to differ from a factory environment, and hence, by obtaining a large number of normal data sets in the actual usage environment, the calculation parameter can be determined appropriately for the actual usage conditions in the customer location. At this time, a device or system is required to determine whether or not the image forming apparatus is in a normal state. The calculation parameter is defined originally to determine the state of a device, but the normal state of the device must be ensured using other means until the calculation parameter is fixed.